Let’s discuss how you can search optimize your website amid a Mobile First Index roll out. Google clearly states that when it comes to mobile first index, only three things come to the consideration : http://www.brainpulse.com/articles/seo-sem/how-to-plan-your-website-seo-mobile-first-index.php

“Although our search index will continue to be a single index of websites and apps, our algorithms will eventually primarily use the mobile version of a site’s content to rank pages from that site, to understand structured data, and to show snippets from those pages in our results.”

I would agree with most of this. But bear in mind, if you want to do mobile SEO well, you can't just make your site mobile-friendly and fast and call it a day.

Mobile SEO is an increasingly complex sub-field of SEO. You want to optimize your content to get featured in Rich Cards, take advantage of AMP, optimize your site for local (a lot of mobile searches are local), etc. Mobile SEO is critical, but because of that there are a lot of players in the space and you need to stand out.

I actually put together a comprehensive mobile SEO guide to help you kick ass at mobile in 2017 and beyond. It goes into depth on all of the above. Feel free to check it out: https://www.coloradoseopros.com/ultimate-guide-mobile-seo